Methods by which extremely high contrast photographic images can be produced using certain kinds of silver halides are known and processes of forming such photographic images are employed in the filed of photomechanical process.
For example, it is known that line images or halftone dot images with high contrast and high optical density wherein image portions and non-image portions are clearly discriminated from each other can be obtained by processing lith type silver halide light-sensitive materials comprising silver chlorobromide (containing at least 50 mol % silver chloride) with a hydroquinone developer having an extremely low effective concentration of sulfite ion (usually not more than 0.1 mol/liter). However, the above-described development process is extremely susceptible to air oxidation due to the low sulfite concentration of the developer and, hence, various efforts and techniques have been made and employed for maintaining the stability of the developer.
Therefore, there has been desired an image-forming system which solves the problem of unstable image formation in the above-described development process (lith development system), which provides superhigh-contrast photographic properties when developed with a processing solution having good storage stability. As is seen in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606 and 4,311,781, a system of forming a superhigh contrast negative image of more than 10 gamma has been proposed, which comprises processing a surface latent image-forming silver halide photographic material containing a specific acylhydrazine compound with a developer having a pH of 11.0 to 12.3 containing 0.15 mol/liter or more of a sulfite preservative and having good storage stability. This novel image-forming system is characterized in that, in comparison with the conventional methods of forming a superhigh contrast image, which permits the use of only silver chlorobromide having a high chloride content, it permits the use of silver iodobromide and silver chloroiodobromide as well as silver chlorobromide.
In general, smaller silver halide grains provide higher optical density of silver halide photographic materials per unit amount of developed silver, whereas larger silver halide grains generally provide higher sensitivity. Therefore, in order to obtain light-sensitive materials having high sensitivity and high optical density, it is necessary to incorporate a large-sized silver halide emulsion in as great an amount as possible per unit area. However, light-sensitive materials containing a large amount of silver halide emulsion require a long time for fixing, washing, and drying in development processing and, as a result, rapid processability is sacrificed. In addition, due to high cost and limited yield and deposits of silver, it has been desired to produce light-sensitive materials using silver in as small an amount as possible.
For these reasons, there has been a long-felt need for silver halide photographic materials having high sensitivity and providing high image density using less silver.
On the other hand, the aforesaid novel high contrast negative image-forming system can cause the unfavorable phenomenon of forming black peppers due to infectious development simultaneously with remarkably high speed and high contrast, which has been a problem in photomechanical processes.
The term "black peppers" as used herein means black spots formed of fine silver deposit produced in non-exposed areas which should essentially be white background.
Black peppers often take place when the concentration of sulfite ion generally used in a developer as a preservative is decreased or when pH is increased, which seriously reduces the commercial value of the products as light-sensitive materials for a photomechanical process. Thus, enormous efforts have been made for removing the black peppers. However, techniques for preventing formation of the black peppers are often accompanied by reduction of sensitivity of gamma (.gamma.). Accordingly, a system has been strongly desired which can prevent black peppers while maintaining high sensitivity and high contrast.
On the other hand, in this field, partial or whole image correction is often conducted by reduction treatment to thereby reduce dot area or thicken or thin the lines or line images for the purpose of reproducing the subtle tone of an original or satisfying artistic expression.
Reducibility is, therefore, an extremely important property required for light-sensitive materials for a photomechanical process. From this viewpoint, too, silver halide photographic materials capable of preventing black peppers and providing high maximum density have been desired.
As one silver halide photographic material having such properties, Japanese Patent Application (OPI) No. 223734/86 discloses a silver halide photographic material containing two kinds of monodispersed emulsions and a hydrazine compound (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). This light-sensitive material is still insufficient in providing high optical density using less silver.